Variable resistor



May 18, 1965 c. c. SNYDER 3,184,696

' VARIABLE RESISTOR Filed March 26, 1962 2 Sheets-Sheet 1 INVENTOR CHARLES C. SNYDER AT TOR NEY y 1965 c. c. SNYDER 3,184,696

VARIABLE RESISTOR Filed March 26, 1962 2 Sheets-Sheet 2 INVENTOR CHARLES C. SNYDER ATTORNEY United States Patent arsasas VARTABLE RESISTGR Charles C. Snyder, Usccola, Inch, assignor to CTS Corporation, Elhhart, Ind, a corporation of Indiana Filed il/iar. 26, 1962, Ser. No. 182,218 Claims. ct. sss 174 This invention relates to variable resistors generally, and in particular to variable resistors adjusted by a rotatable shaft in which the shaft is capable of continuous rotation in one direction.

It is often desirable to have a variable resistor which is adjustable by continuous rotation of its shaft in one direction. This is particularly advantageous when the variable resistor is to be driven by an electric motor, where for economy reasons it is necessary that the electric motor be as simple as possible. Therefore, the variable resistor should be arranged so that it can be rotated continuously in one direction to avoid the necessity to having to reverse the direction of rotation of the electric motor. This also eliminates the dangers inherent in having a stop mechanism built into the motor or the variable resistor. These stop mechanisms are expensive and also introduce the hazard of having the variable resistor or the motor damaged when they run against the stop in either direction.

When constructing a variable resistor of this type, two major problems are encountered. The first problem is the location of the terminals for the center collector. In the conventitonal variable resistor, the resistive path is arcuate but it does not comprise a complete circle. it has an opening which conveniently provides an outlet for the terminal for the center collector. Also since the travel of the movable contact in the conventional control is restricted to the resistive path, the size and shape of the terminal is not critical. When it is necessary to rotate the contact 360, obviously this opening is not available. Further complicating the problem is the fact that it is absolutely necessary that the center collector be maintained within the arcuate confines of the resistive path. The center collector is ussually and preferably concentric with the resistive path. This means that the terminal for the center collector must come either over, under, or across the resistive path to make contact with the center collector.

Another consideration is the fact that all three terminals for the control preferably should lie in the same plane. This means that wherever it is determined to locate the terminal for the center collector, the terminals for the resistive path should be located in the same plane or vice-versa. 7

Therefore, one of the principal objects of this invention is to provide a base for a variable resistor which will allow a center collector which is located wholly within the circular resistive path to be terminated without interfering with the 360 rotation of the contact along the resistive path.

It is an additional object of this invention to provide a base for an electrical resistor which is so constructed that the terminals connected to the circular resistive path and the terminal connected to the center collector encircled by the resistive path extend out from the control in the same plane while allowing 360 rotation of the contact along the resistive path.

The second problem encountered when continuous rotation of the contact is desired is the termination of the resistive element itself. As stated above, it is necessary that the terminals for the resistive element and the terminal for center collector extend out from the control in the same plane. It is also desirable that these terminals not be located in the path of the contact. Lo-

3,l8 i,ii% Patented May 18, 1965 eating the terminals in the path of the contact would not cause any electrical problems but it would cause undue wear of the contact itself. Using any of the conventional methods employed today it is impossible to terminate or electrically connect the terminals to the resistive path without causing a mound or bump to be formed in the path of the contact. These bumps are very detrimental to the contacts, particularly when they are moving rapidly and a carbon button is being used as the contact.

Therefore it is an additional object of this invention to provide a base which will allow the terminals for the resistive path to be located out of the path of the contact.

The invention comprises the use of a novel base and terminal arrangement. The front side of the base is provided with two concentric circular flanges. The outer flange is raised above the inner flange and supports the resistive path. The inner flange serves as centering means for the center collector. In the space between the two flanges three opening are provided; one for each of the three terminals. The back side of the base is generally flat except that a portion of the surface opposite the three opening-s is removed to provide a cavity. Groves extending from the opening to the periphery of the base are also provided in the cavity to help locate the terminals.

The terminals are L-shaped. They are assembled in the base so that one leg extends through one of the openings and the other lies in the groove which intersects the opening. The terminals for the resistive path extend through holes adjacent to but below the ends of the path and are electrically connected thereto by a conductive material. The center collector and its terminal are integrally connected together. For that reason, the

opening through which it passes must be modified somewhat to allow the terminal to be inserted from the front of the base instead of the back. Once the terminals are all in place in the base, the cavity is filled with a member of nonconducting material shaped to fit the cavity. This cavity shaped member holds the terminals in the grooves and it in turn is held in place by an adhesive to complete the assembly.

The invention will now be described in detail making reference to the attached drawings, in which:

FIGURE 1 is an isometric view of a control asembled in accordance with this invention;

FIGURE 2 is a longitudinal cross-section of the control of FIGURE 1;

FIGURE3 is a sectional view taken along line 3-3 of FIGURE 2, assuming that FIGURE 2 is shown in full;

FIGURE 4 is an enlarged view of one end of the resistive path showing the relationship of the resistive path, hop-oil, terminal, and the conductive material connecting the terminal to the hop-oil;

FIGURE 5 is a section take along line 55 of FIG- URE 3;

FIGURE 6 is an isometric view of the front of the base;

FIGURE 7 is an isometric view of the back of the base; and

FIGURE 8 is a section through the base illustrat ng how the cent-er collector and terminal combination is inserted through the opening in the base preparatory to being rotated into its assembled position.

The numeral '19 indicates a variable resistance control generally. The housing of the control is made up of a metal cover 11 which is equipped with tangs 22, a base 12 of nonconductive material, a ground plate 13, and a mounting busing 14. The mounting bushing 14 is preassembled to the ground plate 12 in the manner indicated generally .at 53 in FIGURE 2. The ground plate is held in position against the base and the base in position against the cover 11 by bending over the tangs 22 as shown in FIGURE 1.

Inside the housing formed by these members is a means defining a resistive path or element 13, which is mounted on the base 12, and the collector ring 20. Electrically connecting the resistive path to the collector ring is a wiper means or contact 17 which is equipped with spring arms in engagement with both.

The Contact is carried by the contact carrier 16 which in turn is mounted on the end of the shaft 15. The shaft is rotatably supported by the mounting bushing '14 and is provided with groove 51 and C-ring 52. which engages the end of the mounting bushing 14 and limits the longitudinal movement of the shaft into the control housing. The contact itself serves to limit the outward movement of the shaft.

The base is made of electrically non-conductive material and is provided with the annular flange 26 which supports the resistive path 18. The base also has an annular flange 27 located within the annular flange 26 and concentric therewith. Between the two flanges is a groove 32 in which is located the depending legs 28, which are integrally attached to the center collector and support it above the base. The flange .27 engages the legs 25 and centrally locates the center collector wth respect to the shaft 15 and the resistive path 18.

The base is provided with four passageways extending through it. One, of course, is to provide an opening for the shaft 15 to enter the control. The other three are necessary for the termination of the control as will be explained.

Extending inwardly of the means defining the resistance path 18 is a pair of projecting members 48 and 49 (see FIGURE 6), one of the projecting members being provided with a passageway or opening 23 and the other of the projecting members being provided with a passageway or opening 24-. Each of the projecting members can be a part of the annular flange 26 so long as each of the openings therein is disposed within the means defining the resistance path 18 and adjacent to one of the ends of the resistance path. The other opening is located in between but slightly below the two openings 23 and 24. It is through this larger opening that the terminal for the center collector will extend.

On the opposite side of the base from the flanges a portion of the base is removed adjacent the three openings for the terminals to form the cavity at The cavity 49 extends inward from the periphery of the base and is large enough to encompass the three passageways 23, 24, and 25 but not the opening for the shaft.

In the bottom of the cavity a groove is provided for each passageway which extends from the passageway to the periphery of the base. These grooves are numbered 41, 42, and 43 and are illustrated in FIGURE 7. The terminals are L-shaped and are assembled .so that one leg extends through a passageway and the other lies in the groove leading to the passageway, as shown in FIGURE 5 which is a sectional view through terminal 3t showing how it is electrically connected to the resistive path 18 and structurally connected to the base. The short leg 44 of the terminal 34 extends into the passageway 23 until it approaches the top surface of the flange 26. The long leg 45 of the terminal is placed in the groove 42.

The resistive element 18 and the hop-off 46 are all exaggerated in size for illustrative purposes. Actually the resistive path and the hop-off are both extremely thin films supported by the base and are generally at the most only .a few thousandths of an inch th ck. In fact if the means defining the resistive path is an electrically conductive ceramic material, it may even be less than one-thousandths of an inch in thickness. Also, the hopoff 46 is usually either a fired or screened on silver paint which also produces a very thin film. However, the conductive material 37 used to connect the terminal to the resistive path through the hop-off cannot be applied as a thin film and the size relationship between it and the other components illustrated in FIGURE 5 is fairly realistic. It is for this reason, as pointed out above, that it is important that this terminating material be kept out of the path of the contact 17 if at all possible. Obviously when the contact 17 is riding along an extremely thin film on top of the base '12 the contact pressure must be adjusted to insure good electrical contact between the two. This means that if the conductive terminating material 37 is allowed to cover the end of the resistive paths that the contact 17 has to raise up a considerable amount to pass over these mounds of material. This further deflects the spring arms carrying the contacts which increase the contact pressure which in turn increases the rate of wear of the contact. By locating the openings in the base so that the terminals for the resistive strip are located adjacent to but below the end of the resistive element, the terminating material 37 can be kept out of the path of the contact in the manner shown in FIGURE 4.

Another feature of the invention which can best be seen in FIGURES 5 and 6, is the two projecting members or walls 43 and 49 which surround the openings 23 and 24 respectively. These walls serve two important purposes. First they provide a reservoir for the conductive material used to electrically connect the terminals 30 and 31 to the ends of the resistive path. By prov ding such a reservoir they prevent the conductive material from running down into the groove 32 and providing a shorting path between the resistive element 18 and the legs 28 of the collector ring 20. Second, these walls tend to shield the terminals from the collector ring itself by providing a mass of nonconductive material between the two members.

The terminal 21 is integrally connected to the collector ring as illustrated in FIGURE 8. It is, therefore, necessary to insert the terminal through the base into position from the front side of the base rather than the back side as with the terminals 30 and 31. For this reason the opening 25 is enlarged to allow the terminal to be inserted as illustrated in FIGURE 8 and rotated into the position illustrated in FIGURE 2.

Once these terminals are all in position, the member 50 is placed in the cavity. The material from which the member 5% is made may or may not be the same as the base depending on the desired results. The member is designed to fit the contours of the cavity rather closely to positively hold the terminals in position in the grooves which in turn hold the terminals in position relative to each other. The member is held in place with a nonconductive adhesive 47 which completely fills all open space between the member and the bases. This completes the assembly of the terminals.

From the above description it is apparent to those skilled in the art that the unique design of this base and the method of attaching terminals thereto meets all the objects set out above for this invention.

The invention claimed is:

1. In a variable resistance control, the combination of an electrically nonconducting circular base having a top surface and a bottom surface parallel thereto, means defining a continuous annular path extending around the periphery of the top surface of the base, an arcuate resistance element having its opposite ends spaced from each other and disposed on the means defining the annular path, a rotatable shaft associated with the circular base, the resistance element lying in a plane perpendicular to the axis of the shaft, wiper means carried by the shaft for wiping contact with the arcuate resistance element intermediate the ends thereof, the circular base provided with an opening having one end communicating with the top surface thereof and disposed within the means defining the annular path and positioned to one side of the resistance element so as to be outside the path of travel of the wiper means, said opening being adjacent one end of the resistance element, a cavity provided in the base and communicating with the bottom surface of the base and with the other end of the opening, the opening and the cavity forming an L-shaped passage between the top and bottom surfaces of the base, an L-shaped metal terminal having one leg thereof positioned in the opening and the other leg thereof positioned in the cavity, a conductive material disposed in the opening and electrically connecting the one leg of the L-shaped terminal to said one end of the resistance element, and a nonconductive material disposed in the cavity for securing the other leg of the L-shaped terminal to the circular base.

2. In a variable resistance control, the combination of an electrically nonconducting circular base having a top surface and a bottom surface in parallel relationship to the top surface, means disposed on the top surface of the circular base and having its opposite ends spaced from each other defining an arcuate resistance element, the top surface of the circular base being provided with a recessed portion at least partially encompassed by the arcuate resistance element, a projecting member adjacent to one of the ends of the arcuate resistance element and disposed in the recessed portion of the base, a passageway in the projecting member having one end communicating with the top surface of the base, the base being provided with a cavity communicating with the other end of the passageway and the bottom surface of the base, the pas sageway and the cavity forming an L-shaped passage between the top and bottom surfaces of the base, an L- shaped terminal partially disposed in the cavity and having a part thereof disposed in the passageway, means defining a conductive path disposed on the top surface in overlapping relationship with respect said one end of the resistance element, a conductive material bonded to the part of the terminal in the passageway and to the conductive path for electrically connecting the resistance element to the L-shaped terminal, and a nonconductive material disposed in the cavity and bonding the terminal therein to the base.

3. In a variable resistance control, the combination of an electrically nonconducting circular base having a top surface and a bottom surface in parallel relationship to the top surface, means disposed on the top surface of the circular base defining an arcuate resistance element, the top surface of the circular base being provided with a recessed portion encompassed by the arcuate resistance element, a projecting member adjacent to the arcuate resistance element and disposed in the recessed portion of the base, a passageway in the projecting member, having one end communicating with the top surface of the base, the base being provided with a cavity communicating with the other end of the passageway and the bottom surface of the base, the passageway and the cavity forming an L-shaped passage between the top and bottom surfaces of the base, an L-shaped terminal partially dis posed in the cavity and having a part thereof disposed in the passageway, means defining a conductive path disposed on the top surface in overlapping relationship with respect to a portion of the resistance element, and a conductive material bonded to the part of the terminal in the passageway and to the conductive path for electrically connecting the resistance element to the L-shaped terminal.

4. The control of claim 3, wherein the one end of the passageway communicating with the top surface of the base is substantially larger than the cross section of the part of the terminal disposed therein to provide sufficient space for the conducting material deposited therein and electrically connected to the terminal.

5. In a variable resistance control, the combination of an electrically nonconducting circular base having a top surface, a bottom surface, and a centrally disposed aperture, an annular flange projecting from the top surface, means disposed on the annular flange defining an arcuate resistance element having its opposite ends spaced from each other and lying in a plane perpendicular to the axis of the aperture in the base, collector means carried by the base in spaced relationship to the resistance element, the resistance element and the collector means being concentric with the centrally disposed aperture, a shaft journalled in the aperture in the base, means carried by the shaft for wiping contact with the resistance element intermediate its ends and the collector ring, the circular base being provided with an opening having one end adjacent to one of the ends of the resistance element and communicating with the top surface of the base, a cavity provided in the base and communicating with the bottom surface thereof and with the other end of the opening, the opening and the cavity forming an L shaped passage between the top and bottom surfaces of the base, an L-shaped terminal having one leg thereof isposed in the opening and the other leg thereof in the cavity, means defining a conductive path disposed on the annular flange in overlapping relationship with respect said one end of the resistance element, a conductive material bonded to the one leg of the L-shaped terminal and to the conductive path for electrically connecting the resistance element to the L-shaped terminal, and a nonconductive material bonding the other leg in the cavity.

References Cited by the Examiner UNITED STATES PATENTS 2,389,750 11/45 Turner et al 338--l74 X 2,606,985 8/52 De Bell 338-174 2,873,336 2/59 Tassara 338-174 3,012,215 12/61 Hartman et al. 338-329 X 3,117,298 1/64 Grunwald 338312 FOREIGN PATENTS 532,710 1/41 Great Britain.

RICHARD M. WOOD, Primary Examiner. 

1. IN A VARIABLE RESISTANCE CONTROL, THE COMBINATION OF AN ELECTRICALLY NONCONDUCTING CIRCULAR BASE HAVING A TOP SURFACE AND A BOTTOM SURFACE PARALLEL THERETO, MEANS DEFINING A CONTINUOUS ANNULAR PATH EXTENDING AROUND THE PERIPHERY OF THE TOP SURFACE OF THE BASE, AN ARCUATE RESISTANCE ELEMENT HAVING ITS OPPOSITE ENDS SPACED FROM EACH OTHER AND DISPOSED ON THE MEANS DEFINING THE ANNULAR PATH, A ROTATABLE SHAFT ASSOCIATED WITH THE CIRCULAR BASE, THE RESISTANCE ELEMENT LYING IN A PLANE PERPENDICULAR TO THE AXIS OF THE SHAFT, WIPER MEANS CARRIED BY THE SHAFT FOR WIPING CONTACT WITH THE ARCUATE RESISTANCE ELEMENT INTERMEDIATE THE ENDS THEREOF, THE CIRCULAR BASE PROVIDED WITH AN OPENING HAVING ONE END COMMUNICATING WITH THE TOP SURFACE THEREOF AND DISPOSED WITHIN THE MEANS DEFINING THE ANNULAR PATH AND POSITIONED TO ONE SIDE OF THE RESISTANCE ELEMENT SO AS TO BE OUTSIDE THE PATH OF TRAVEL OF THE WIPER MEANS, SAID OPENING BEING ADJACENT ONE END OF THE RESISTANCE ELEMENT, A CAVITY PROVIDED IN THE BASE AND COMMUNICATING WITH THE BOTTOM SURFACE OF THE BASE AND WITH THE OUTER END OF THE OPENING, THE OPENING AND THE CAVITY FORMING AN L-SHAPED PASSAGE BETWEEN THE TOP AND BOTTOM SURFACES OF THE BASE, AN L-SHAPED METAL TERMINAL HAVING ONE LEG THEREOF POSITIONED IN THE OPENING AND THE OTHER LEG THEREOF POSITIONED IN THE CAVITY, A CONDUCTIVE MATERIAL DISPOSED IN THE OPENING AND ELECTRICALLY CONNECTING THE ONE LEG OF THE L-SHAPED TERMINAL TO SAID ONE END OF THE RESISTANCE ELEMENT, AND A NONCONDUCTIVE MATERIAL DISPOSED IN THE CAVITY FOR SECURING THE OTHER LEG OF THE L-SHAPED TERMINAL TO THE CIRCULAR BASE. 